Issue 1119 changing spectral axis#1136
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set_spectral_axis modifies the units, frame or Doppler convention of the spectrum. with_spectral_axis_unit adds the observer and target attributes back to the new spectrum object to make it compatible with dysh.spectra.Spectrum objects.
Adds set_spectral_axis to the user guide.
mpound
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Jun 24, 2026
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The example fails for me because specutil.Spectrum.with_spectral_axis_unit uses velocity_convention as the keyword not doppler_convention so passing *args raises an exception.
Cell In[6], line 4
2 s1 = Spectrum.fake_spectrum()
3 s1.set_spectral_axis(unit="km/s", doppler_convention="radio") # Changes the Spectrum in place.
----> 4 s2 = s1.with_spectral_axis_unit("km/s", doppler_convention="optical") # Creates a new Spectrum.
File /bigdisk/src/dysh/src/dysh/spectra/spectrum.py:1101, in Spectrum.with_spectral_axis_unit(self, *args, **kwargs)
1100 def with_spectral_axis_unit(self, *args, **kwargs):
-> 1101 spec = super().with_spectral_axis_unit(*args, **kwargs)
1102 spec._observer = self.observer.copy()
1103 spec._spectral_axis.observer = self.spectral_axis.observer.copy()
TypeError: OneDSpectrumMixin.with_spectral_axis_unit() got an unexpected keyword argument 'doppler_convention'
specutils.__version is '2.3.0'
The tests pass, though.
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mpound
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Jun 28, 2026
| # Keep docstring empty to re-use the one from specutils. | ||
| # Keeping the specutils doc introduces yet another name | ||
| # for what we call `doppler_convention`, `velocity_convention`. | ||
| # This is a source of frustration... |
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Because specutils does not follow the astropy parameter name 'doppler_convention' in SpectralQuantity
mpound
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Jun 28, 2026
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Cell 6: sdfits["CTYPE1"][0] returns nan
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Also, sometimes notebook plots just hang but I don't belive that has anything to do with this PR.
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Adds Spectrum set_spectral_axis and with_spectral_axis_unit (overloads the specutils method).
set_spectral_axismodifies the units, frame or Doppler convention of the spectrum.with_spectral_axis_unitadds the observer and target attributes back to the new spectrum object to make it compatible withdysh.spectra.Spectrumobjects.Example: